# DISC SPRINGS WITH CONTACT FLATS AND REDUCED THICKNESS

For disc springs with a thickness of more than 6.0mm, DIN 2093 specifies small contact surfaces at points l and lll in addition to the rounded corners. Figure 5 shows a schematic cross-section of a spring in group 3 as per DIN 2093. The corresponding springs of our factory standard are also manufactured in the same manner.

**Figure 5 - click to enlarge**

These contact flats improve definition of the point of load application and, particularly for spring stacks, reduce friction at the guide rod. The result is a considerable reduction in the lever arm length and a corresponding increase in the spring load. This is in turn compensated for by a reduction in the spring thickness from t to t’.

When calculating disc springs with contact flats and reduced thickness, the factor K_{4} must be calculated using formula 6, and t replaced with t’ and h_{o} with h_{o}’ = l_{o} – t’ in the equations 7 to 16.

The reduced thickness t’ is specified in accordance with the following conditions:

- The overall height lo remains unaltered
- The width of the contact flats is to be approximately 1/150 of the outside diameter
- The spring load for a reduced thickness spring must be the same at s = 0.75 h
_{o}as for an unreduced spring

The dimension t’ is specified for those discs springs contained in DIN 2093. The mean factor t’/t is:

Series |
A |
B |
C |

t’/t | 0.94 | 0.94 | 0.96 |

For other springs the factor for t’/t is dependent on the dimensional ratio δ and h_{o}/t from figure 6. The curves were calculated for disc springs with δ_{OM} = -1600N/mm^{2}. For springs with different stress s_{OM}, we would ask you to contact us on 01202 339559.

As the overall height is not reduced, springs with reduced thickness inevitably have an increased flank angle and a greater cone height h_{o}’ than springs of the same nominal dimension without reduced thickness. Therefore, the characteristics curve is altered and becomes more curved. Figure 7 shows the characteristic curves for springs of the series A, B and C as per DIN 2093 with and without contact flats and reduced thickness.

**Figure 6 - click to enlarge**

**Figure 7 - click each image to enlarge**